Maybe. Ethos is a reflection of the culture of the period. If he was focusing on change, one could argue his culture is similar to those before him who stood for change.
I am not so certain that change alone is culture, however, others will disagree. Ethos is more to me than change. Janet Joplin, as radical a change can be, did not to me represent a distinct ethos. However, she was a subset of the Hippie/Rock Ethos of the sixties and seventies.
Some folks will look at fashion (width of mens ties, or womens hairdos) and see a culture in itself, and label this an ethos. For myself, I am not so certain.
So yes, some would argue the culture of change could use Roosevelt and Kennedy as models. Often folks forget that Kennedy got through congress very little change legislation, it took LBJ as president to do that.
I don't have the text of Sen. Obama's speech, but if you're clear on the meaning of "ethos," you'll find it easier to locate instances of ethos in his speech, if there are any.